DE102014214640A1 - Method for producing a component from heat-treated cast iron - Google Patents

Abstract

The invention relates to a method for producing a tempered component made of heat-treated cast iron (AGI). According to the invention, a base body made of cast iron is provided for this purpose, which may preferably already have the shape of an engine block. The main body is first subjected to a mechanical pre-processing (H3a), in whose framework, for example, any holes can be introduced. Subsequently, the already mechanically processed base body is tempered by this is subjected to a suitable heat treatment (H2), so the special heat treatment. A post-processing, ie the creation of the final dimension can follow.

Description

The present invention relates to a method for producing a component from heat-treated cast iron.

Metallic components made of cast iron have the advantage over such components produced by a purely mechanical treatment that their shaping takes place substantially already during the casting. Here, the casting material is heated to its transition into the liquid phase and then poured into a mold. By cooling it solidifies this, so that a basic body with a predetermined shape is formed. In particular, more complex component shapes can be created at all or at least more economically. The latter usually requires higher quantities, since the effort and the associated costs for the necessary forms are comparatively high.

Typically, suitable iron alloys having a high carbon content are used to make cast components. This can be present as graphite or as cementite. Depending on the type of carbon present, a distinction is made in gray cast iron (graphite) or white cast iron (cementite). With regard to the mechanical properties of such cast iron, graphite plays a role, since cast iron is further subdivided into those with lamellar graphite or nodular graphite.

As a result of the advantages described at the beginning, cast iron is increasingly being used in the automotive industry and here in particular in the field of engine production. Following the general trend of downsizing, which essentially means reducing the weight while maintaining strength properties, the material cast iron is also coming into focus. In fact, it was also possible to develop for this new production process, with which higher strength values can be achieved. Thus, various possibilities of heat treatment of cast iron are now known, in addition to its increase in strength at the same time to achieve an increase in the elongation at break properties. In this context, a special heat-treated cast iron was developed, which is also known as Austempered Gray Iron or AGI briefly, which has a very high strength with good elasticity and high alternating strength and resistance to wear. The EP 1 032 770 B1 For example, it deals with an AGI in connection with brake discs. However, only the brake disk body itself is formed from the AGI, wherein the wheel hub of the brake disk is formed of a different material, for example of a normal cast iron, cast steel or formed steel with a tensile strength greater than 170N / mm ² . Both materials are joined by composite casting of the wheel hub with the brake disc body to form a cohesive compound in the connection area. After twisting and curing this component is subjected to a bainitic curing and then ground.

However, the above advantageous properties (e.g., higher strength) sometimes have far-reaching disadvantages for manufacturing practice. Here it is the processing, in particular the mechanical processing of components made of special heat treated cast iron, which is very expensive due to the increased strength and hardness. Here, the long processing times and the wear on the machining tools are essentially to name.

In view of the inherently positive properties of heat-treated, ie, tempered cast iron, its processing therefore leaves room for improvement.

Against this background, the invention has the object to further develop a method for producing a component made of heat-treated cast iron in order to minimize the total associated production costs and thus to improve the competitiveness of components made of intergraded cast iron in terms of manufacturing costs.

According to the invention, this object is achieved by a manufacturing method having the features of claim 1. Further, particularly advantageous embodiments of the invention disclose the respective subclaims.

It should be noted that the features listed individually in the following description can be combined with one another in any technically meaningful manner and thus show further embodiments of the invention.

After that, a method is presented, which is suitable for the production of a component made of heat-treated cast iron. For the purposes of the invention, heat treatment of the cast iron is understood as meaning a special heat treatment in which a completely ausferritic microstructure is established in the case of an ideally 100% ferritic hardening of the relevant component. The special heat treatment according to the invention involves quenching in a salt bath.

According to the invention, a base body made of cast iron, ie an engine block, is provided for this purpose. This can be generated beforehand by a suitable casting process. In addition to possible Entgratungsarbeiten the invention aims in particular to the fact that the cast base body, so the engine block requires further processing. For this purpose, the not yet heat-treated body is first subjected to mechanical processing. According to the first mechanically processed base body is then subjected to the special heat treatment only to effect its remuneration. In other words, the transformation of the cast iron into a tempered cast iron takes place only after the unfired basic body has been mechanically processed.

The resulting advantage lies essentially in the fact that in this way a rapid and low-wear mechanical processing of the body can be done at a time at which this still has no increased strength properties. Only after the mechanical processing has taken place, the actual remuneration of the body is carried out by way of special heat treatment, as defined above.

Particularly preferably, the mechanical processing in question in the sense of a pre-processing can be considered, which of course does not necessarily exclude possible reworking, in particular mechanical reworking.

According to the invention, it is provided that, within the scope of the mechanical processing, honing of the base body can be carried out at least in regions. Hone is understood herein to mean a fine machining of surface areas. This is usually done mechanically by contact with a corresponding scurfing tool, such as a Hohnahle. Of course, the honing can also take place in the sense of a removal, as it can be carried out for example by the use of a laser.

Furthermore, as part of the mechanical processing of the base body, at least one bore will be arranged in or on this. In the present case, a bore is understood as meaning both a through-bore and a partial bore, for example a blind hole.

It should be noted that said honing and / or drilling can also take place in the context of any subsequent processing subsequent to the special heat treatment, that is to the remuneration of the base body. In this respect, the mechanical processing named here can also be understood in the sense of a post-processing. This in particular against the background, since honing mostly and drilling is sometimes used to improve the dimensional and / or dimensional accuracy of component areas.

Advantageously, the base body can only be heated to a temperature of e.g. 850 ° C to 950 ° C are heated. Its heating can be carried out particularly preferably in the context of its special heat treatment, as defined above. In this context, it is envisaged that the heating can take place in a suitable oven. Particularly preferably, the heating can take place under protective gas. Taking into account, for example, the wall thickness and / or the chemical composition of the still ungutted base body, an appropriate determination of the holding time is made, so that the above properties (ausferritische microstructure, ausferritisches hardening) set.

Following the heating of the already mechanically processed body is provided that this can be cooled in the context of special heat treatment after its heating in a salt bath. Preferably, the temperature of the salt bath for the conversion may be in a temperature range of 220 ° C to 450 ° C. Further preferably, the conversion time may well be several hours. Advantageously, the conversion time is set to give preferably over 90%, ideally 100% conversion to ausferritic cast iron.

The finished component is an engine block. In this way, the advantageous properties of the heat-treated cast iron can be combined with the inventive simple and inexpensive production for engine blocks.

Although the invention of no significant or at least homogeneous shape change of the body during its special heat treatment. However, it is considered advantageous if a possible change in shape can already be taken into account by its subsequent special heat treatment, ie compensation, during the mechanical processing of the basic body. For this purpose, for example, any openings in the context of taking place before the special heat treatment mechanical processing can be performed correspondingly smaller or larger, so that they already have a high dimensional stability after the special heat treatment.

According to an advantageous development of the invention, the already tempered by the special heat treatment body can subsequently at least partially reworked. As a result, for example, surface areas of the base body can be brought to their final dimensions.

Although the post-processing here, too, are somewhat counteracted by the improved properties of the now heat-treated cast iron, but to a lesser extent. In other words, the main mechanical processes have already taken place at this time, so that the post-processing can essentially only be reduced to the formation of the desired final dimensions.

In connection with the post-processing, it is further contemplated that at least one opening of the base body, which has already been tempered by the special heat treatment, can be subsequently at least partially reworked to its final dimension only at this time. In the context of the invention, an opening is also understood to mean a hole. In addition, reference is made to the previous comments regarding honing and / or drilling.

Also, as part of the post-processing, the at least one opening of the base body, which has already been tempered by the special heat treatment, can then be at least partially provided with a thread. As a result, a high dimensional accuracy of the required thread is achieved, at the same time little effort.

1 shows a manufacturing process by way of example of a motor block according to the prior art. Further advantageous details and effects of the invention are described below 2 explained in more detail. It shows:

2 the diagram 1 taking into account the method according to the invention.

1 shows in stylized form the typical production process for components from normal (line GG, solid) and made of heat treated cast iron (line AGI, solid). This ranges from casting H1 of the main body over its compensation by a special heat treatment H2 and the subsequent mechanical processing H3 up to the finished component. The production process shown in diagram form gives information about the required time T with respect to the costs U, which extend mutatis mutandis along the ordinate on its abscissa.

The upper curve stands for the production of any part made of special heat-treated cast iron component AGI, whereas the lower curve stands for the production of a conventional cast-iron component GG. As can be seen, the costs for producing components made of heat-treated cast iron are consistently higher than in conventional cast-iron components made of cast iron (GG). Here, in addition to the heat treatment H2, it is in particular the mechanical processing H3 which causes said high costs. This for the reason that the heat-treated body is much harder, which leads to the processing tools to considerable wear, so they must be replaced early, so need to be procured new.

2 now shows the achievable with the inventive method result in terms of cost. For better distinction, the component made of special heat-treated cast iron, that is, the motor block with its downstream processing of the special heat treatment, was referred to herein as AGIn. The graph AGIn is dotted. The component, so the engine block can be made visible cheaper with the method according to the invention.

The cost savings are here in particular in the mechanical processing H3, which according to the invention is divided into a pre-processing H3a and a post-processing or a finish H3b. Since the substantial processing takes place in the context of the pre-processing H3a, the effort and thus the costs in the post-processing or the finish H3b significantly reduced. However, it has to be considered that the upstream preprocessing process also already incurs costs, whereby the graph AGIn initially disadvantageously lies above the graph AGI in the region H3a and H2. However, this initially disadvantageous cost factor is more than offset by the lower cost of machining and the lower wear of the processing tools after the special heat treatment, even significantly reduced, as the double arrow between the graphs AGI and AGIn sets out. The double arrow represents the cost advantage of the procedure according to the invention over the conventional procedure.

LIST OF REFERENCE NUMBERS

• AGI

  Graph for conventionally machined component

  Agin

  Graph for inventively processed component

  GG

  Cast iron (without quality)

  H1

  Production step casting

  H2

  Production step heat treatment

  H3

  Production step mechanical processing (general)

  H3a

  Production step mechanical pre-processing

  h3b

  Production step mechanical post-processing

  T

  Time

  U

  costs

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1032770 B1 [0004]

Claims (6)

Method for producing a component of heat-treated cast iron, comprising at least the steps Casting a body of cast iron, Mechanical preprocessing (H3a) of the base body, wherein the mechanical pre-machining (H3a) comprises at least partial honing and creating at least one hole, Special heat treatment of the pre-machined base body, whereby the special heat treatment results in an ausritritic microstructure, finishing (H3b) of the base body to its final dimension. A method according to claim 1, characterized in that the mechanically pre-machined (H3a) base body is heated to a temperature of 850 ° C to 950 ° C as part of its special heat treatment (H2). A method according to claim 1 or 2, characterized in that the mechanically processed base body is cooled in the course of its special heat treatment (H2) after heating in a salt bath. Method according to one of the preceding claims, characterized in that the base body is formed in the form of an engine block. Method according to one of the preceding claims, characterized in that in the mechanical pre-processing (H3a) a change in shape of the base body is taken into account by its subsequent special heat treatment, ie compensation. Method according to one of the preceding claims, characterized in that at least one opening of the by the special heat treatment (H2) already annealed base body is then at least partially provided with a thread, in particular by a mechanical processing (H3b).

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